Image exposure and development method

ABSTRACT

The image exposure and development method of this invention comprises: the steps of exposure of a sensitive medium which is developable by the deposition of atoms thereon, feeding the exposed medium to wrap around a major portion of the circumference of spaced discs, and directing a vapor flux between the discs to impinge upon the medium so that the latent image thereon is developed by selective acquisition of the metal onto the surface.

11 States Patent Kaspaul 51March 20, 1973 54] HMAGE EXPOSURE AND 3,489,560 1 1970 Joseph ..117 17.5 x DEVELOPMENT METHOD 3,585,917 6/1971 Griffith ..95/89 R 3,565,523 2/1971 Davis et al. ..95/89 G [75] Inventor: Alfred F. Kaspaul, Malibu, Cal1f.

[73] Assignee: Hughes Aircraft Company, Culver Primary Examiner-SamuelS. Matthews City, Calif. Assistant Examiner-Fred L. Braun [22] Filed Feb 4 1972 Attorney-W. H. MacAllister et al.

[21] App]. No.: 223,533 57 ABSTRACT Related US. Application Data The image exposure and development method of this {63] continuatiommpan of Sen No 115 943 Feb. 17 invention comprises: the steps of exposure of a sensi- 1971 Pat. 3 664 249 tive medium which is clevelopable by the deposition of atoms thereon, feeding the exposed medium to wrap 52 11.5.01. ..355/77, 96/48 R, 117/175 around a major portion of the circumference of 51 Int. Cl. ..G03b 27/32 Spaced discs, and directing a vapor flux between the [58] Field of Search...355/27, 77, 106, 132; 95/89 R, discs to impinge upon the medium so that the latent 95/89 G, 94 G; 96/48 R; ll7/17.5; 118/49 image thereon is developed by selective acquisition of the metal onto the surface. 56] References Cited 6 Claims, 11 Drawing Figures PATENTEDHARZOIHH SHEET 2 [IF 7 PATENTEUmzmm sum 30F 7 Fig. 40.

mE o muotam *0 59:52

Time

v PATENTEUMAR201975 SHEET U 0F 7 PATEUIKUMAMO m5 SHEET 8 BF 7.

Fig. 9

. PRIOR ART IMAGE EXPOSURE AND DEVELOPMENT METHOD CROSS REFERENCE This application is a continuation-in-part of patent application Ser. No. 115,943, filed Feb. I7, 1971, now U.S. Pat. No. 3,664,249, which, in turn, was a division of the application which resulted in U.S. Pat. No. 3,585,965.

BACKGROUND This invention is directed to a method for exposing and developing a photosensitive medium to produce a latent image thereon and to develop the latent image into a visible image by means of the selective deposition of metal atoms thereon from a vapor.

A number of prior art processes for the recording of information and subsequent formation of visible images employ the selective deposition of various materials into latent images. An example of this is found in A. F. Kaspaul et al. U.S. Pat. No. 3,235,398, granted Feb. 15, I966. A number of other inventions are directed to the same general type of process. These processes employ the selective deposition of metal atoms to create the visible image. A. F. Kaspaul et al. U.S. Pat. No. 3,l40,143, granted July 7, 1964, describes the use ofa metal chosen from Group Il-B of the periodic system as a metal which can be employed with the particular substrate disclosed therein. Selective deposition can be accomplished on suitable substrates by the employment of a variety of other materials as they are discharged from a boiler or any other suitable source. Additionally, a metal chosen from Group I-B or magnesium is suitable and can be employed in the same way. In other cases, the developer material is provided by the dissociation of a metal-containing compound, such as silane. Furthermore, cadmium sulfide, lead sulfide, bismuth trioxide may be deposited in imagewise fashion to produce active elements for microcircuitry applications, as described in A. F. and E. E. Kaspaul U.S. Pat. No. 3,333,984, granted Aug. 1, 1967. Additionally, while the three cited prior patents describe the selective deposition of metals, metal chalcogenides, etc., for image production, such deposition can be employed for other purposes, such as providing a conductive path, or the like. I

The prior art teachings are directed to batch-type processing, as well as toward continuous applications. However, they have not resulted in efficient employment of the vaporized materials at high processing speeds. Accordingly, in the prior art applications, a sizeable fraction of the developer" is deposited within the development chamber rather than onto the substrate. Thus, in continuous usage, material is wasted and frequent cleaning is necessary.

SUMMARY In order to aid in the understanding of this invention, it can be stated in essentially summary form that it is directed to an image exposure and development method which includes the steps of exposure of a nucleation-sensitive material to create a latent image thereon, followed by continuously feeding the medium to a development chamber which is defined by first and second circular closure plates which define the ends of LII the development chamber and wrapping the medium substantially around the closure plates to form the radial confines of the chamber, and development of the latent image by directing a metal vapor source onto the exposed medium to make the latent exposure visible.

Accordingly, it is an object of this invention to provide an image exposure and development method which is arranged for the exposure of and subsequent development of various medium by the deposition thereon of selected materials to form a visible image faithfully reproducing the information exposed on the medium to form latent, invisible images on the medium. It is a further object of this invention to provide an image exposure and development method wherein a portion of the chamber wall is formed by other than the medium and is at such conditions, and the developing vapor flux is adjusted to such a rate that stable deposition does not take place on any of the walls of the chamber except the wall formed by the medium. It is still another object of this invention to provide an image exposure and development method which employs first and second spaced discs and the medium embraces a large portion of the circumference of the discs to define the image exposure and development method and apparatus therein. It is a further object to provide an exposure and development method wherein continuous development is accomplished at nearly percent efficiency. Other objects and advantages of this invention will become apparent from a study of the following portion of the specification, the claims, and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of a recording and playback console employing the preferred embodiment of a structure for employing the image exposure and development method of this invention.

FIG. 2 is an enlarged partial section taken generally along the line 22 of FIG. 1.

FIG. 3 is a partial section taken generally along the line 3-3 ofFIG. 2.

FIGS. 4a, 4b, and 4c are graphs showing various conditions under which selective deposition of atoms and molecules will occur.

FIG 5 is a schematic view of the development chamber of this invention showing development vapor paths.

FIG. 6 is a schematic view of a prior art development chamber showing development vapor paths.

FIG. 7 is a schematic view of the development chamber of this invention showing an optical wiper therein.

FIG. 8 is a section on the line 88 of FIG. 7.

FIG. 9 is a schematic view of another embodiment of the development chamber of this invention.

DESCRIPTION A recording and playback console 10 incorporates the development chamber 12 of this invention Console 10 includes housing spaces 14 and 16 for electronics. It is electrically connected and arranged to receive an electronically defined image which can be visually displayed on the face of cathode ray tube 18. In other words, the console receives images and sound in the' form of electronic signals resulting from various sources commonly employed in conventional television practice. The purpose of the console is to receive, record, and to play back these signals in a desired line frequency.

An electron source 20 produces a modulated beam 22 in accordance with the input signals. Beam 22 is focused and deflected by any conventional electrostatic or electromagnetic means, such as focusing and deflection means 24. However, rather than producing orthogonal scan, only lateral scan corresponding to the horizontal scan on the image is produced by the deflection means. Housing 26 encloses the beam and is pumped to a suitable low pressure at the pump connections indicated for satisfactory beam performance. Drift tube 27 permits beam passage.

As is seen in FIG. 2, tape deck 28 includes a supply of recording tape on reel 30. The tape 32 passes around exit guide roll 34 through slot 36 into a very narrow gap of chamber 38. Capstan 40 rotates simultaneously with capstan 66 within chamber 38, wrapping the tape 32 around its circumference. The width of slot 36 and the clearance around recording tape 32 as it moves around the capstan 40 within chamber 38 is minimized to reduce pumping requirements. Opening 42 in tape deck 28 permits beam 22 to impinge upon media 32 as it moves past opening 42 to thus create a latent image on the recording media. Since tape deck 28 and opening 42 are evacuated to different vacuum levels, the narrow spaces in chamber 38 are sufficient to maintain the desired pressures for each area.

Differential pumping of the recording/readout chambers and the respective gun areas is preferably utilized to minimize the size requirements of the vacuum equipment. FIG. 2 shows an arrangement whereby the gun areas may be held at Torr with a 2 inch diffusion pump by connection to port 39, whereas the recording/readout chambers are maintained at 10 Torr with a 3 inch booster pump by connection to port 41. Development chamber 44 and tape reel chambers of the tape deck 28 operate at 10' and 10 Torr, respectively, by use of forepumps connected to ports 43 and 45.

From chamber 38, the media 32 passes into the stationary development chamber 44 in which the rotating development chamber 12 is located. As seen in FIG. 3, chamber 44 is closed by transparent cover 46 so that the progress of development can be observed. Bearing post 48 is centrally mounted in recess 44, and hub 50 is rotatably mounted thereon. Circular discs 52 and 54 are mounted upon hub 50 so as to rotate therewith. Preferably, upper disc 54 is conveniently removable from the hub and is transparent for visibility purposes. Tape 32 passes around discs 52 and 54 so that the edges of the medium are engaged thereby, and the discs, together with the hub, are rotated as the medium passes through the stationary development chamber 44. Tape 32 engages around a substantial part of the circumference of the discs, as shown in FIG. 2, to define the rotating development chamber 12 enclosed by the medium and the discs.

Source 56 is the source of atoms and/or molecules for the development of the latent images contained within the medium 32. Source 56 is conveniently a heated coil or mesh which is connected by leads 58 to the secondary of transformer 60. Energization of leads 62 to the primary of transformer 60 causes high current flow through the coil which forms source 56, thereby heating it to the proper temperature. When the coil or mesh is plated with the metal to be vaporized, such as zinc or cadmium, 10 watts is sufficient to develop a 35 mm tape at 36 inches/second, and one coil or mesh can have sufficient material to develop more than several thousand feet of tape. Of course, other vapor sources may be employed, e.g., a small boiler could be used to supply the required vapor for many tape reels. Source 56 is preferably positioned so that it is spaced equal distance from all points of the tape as the tape is wrapped around the discs to form the development chamber.

The developer source may be of any type and shape and will successfully operate as long as it is centrally located. Of course, an eccentric positioning is possible, if one adjusts the efflux pattern accordingly.

After leaving stationary development chamber 44, the now developed tape is transported to chamber 64 where it engages around capstan 66. After leaving capstan 66, tape 32 passes through slot 68 and around guide roll 70 to be wound on tape reel 72. If reading of the image is required immediately following recording and development, it may be accomplished with the readout gun 74 scanning across the tape on capstan 66. Electron gun 74 in housing 76 directs an electron beam 78 onto the image-carrying medium. Focus and deflection means 80 scans the electron beam laterallyacross the tape as it moves past opening 82. As a result of electron impingement, photons are emitted in accordance with the'image content of the medium. These photons are focused by mirror 84 onto photomultiplier 86. The image is thus returned to an electronic signal and can be rebroadcast in a different line frequency and/or cathode ray tube 88. Housing 76 is suitably evacuated for proper electron beam conditions, andthe narrow spaces around the medium in chamber 64 permit the maintenance of a proper vacuum with minimal pumping equipment.

The usefulness of this invention may best be understood by exposing a given surface to an incident flux of atoms and/or molecules from a molecular oven or other vapor source. Atoms and/or molecules will condense upon the surface, at first moving about it in random fashion. They are eventually captured by active sites to form a stable deposit, or re-evaporated from the surface after a certain time has elapsed. At low incident rates, a certain number of atoms will be found upon the surface at any given time so that the equilibrium concentration is reached as soon as the re-evaporation rate equals the incident flux. At equilibrium,

g (In/N log A (0.434) daad/RT n, Incident flux, [atoms cm sec' n, Re-emitted atoms, [atoms cm sec- N Number of surface adsorbed atoms, [atoms A Frequency constant z 10 for most metals nd Estimated heat of adsorption, [Kcal mole"] R Gas constant [1.987 cal deg mole"] T =Temperature in degrees Kelvin [K] Using zinc for the incident atoms and a glass surface held at 300 K as the receptor,

Using this value, surface concentrations of 10 or 10 atoms/cm are obtained with incident rates of 10 or 10 atoms/cm sec. It may be assumed that up to surface coverages of 10 (6 qd/ pl; p1 number of possible surface sites in an orderly lattice) no stable twins or even triplets will be produced which have a much longer lifetime than single atoms, thus all atoms will eventually leave the surface, especially upon cessation of the incident flux. In FIG. 4a, curves 90 and 92 indicate this for the two concentrations of 10 and atoms/cm*, respectively. Hence, the two glass discs of the development chamber should be free of zinc deposits as long as the surface coverage is kept below 10- and spurious nucleation centers are avoided. FIG. 7 shows a simple solution for the prevention of random nucleation centers in the rotating development chamber.

As previously indicated, the recording tape containing the latent images forms a substantial portion 'of the development chamber and is therefore exposed to the incident flux of zinc atoms, as long as it surrounds the two glass discs and the developer source. During this time interval, atoms and/or molecules will condense and re-evaporate from its surface which has, with the exception of the latent images, quite similar surface properties as those of the glass discs. Hence, no-condensation occurs upon the background of the medi um.

However, electrons previously impinged upon the medium have created latent images characterized by areas of much greater heat of adsorption for zinc. At an incident flux of about 10 atoms/cm sec., these invisible images develop into visible images, in less than one second, if one assumes that 4), is about 12 K cal/mole for an average portion of the latent image, thus The corresponding surface concentration amounts to nearly l0 atoms/cm (0 10') which is much too large to maintain equilibrium condition, hence rapid formation of twins, triplets and stable cluster occurs and continuous film growth is only a matter of time.

Because the previous electron beam incidence upon the tape has modulated the number of nucleation sites, their effective energy and distribution, (b varies with the information content and one obtains a time dependence of the onset of permanent condensation. This is illustrated in FIG. 41; by curves 94 and 96, assuming a constant incident rate. Curve 94 represents a large exposure to electrons, curve 96 a smaller amount of irradiation, and curve 92 the unexposed background of the tape. The critical surface concentration of about l0 atoms/cm was found experimentally; at this point, the re-evaporation rate drops rapidly to zero and every incoming atom must be captured. By carefully controlling the zinc flux and the development speed, all zinc atoms are eventually deposited upon the recording tape without any loss of material to adjacent areas. Furthermore, by the very nature of the rotating development chamber, any rise of the incident rate does not precipitate the deposition of zinc on unwanted areas, because the process is self-regulating. This is best explained by FIG. 4c.

As shown, the tape enters the rotating development chamber on the left and is immediately exposed to a uniform zinc flux. Depending upon the image content, it will take a certain time for even the most energetic centers to take full control over the deposition process, faithfully reproducing the desired information.

For all practical purposes, the time interval from the first exposure of the tape to the zinc vapor to the onset of barely visible images ranges from about 0.25 to 0.75 of the total time spent in the development chamber.

Normally, the onset of visible condensation is chosen to be at about midpoint in the development chamber by adjusting the incident rate accordingly, hence a rise or fall of the number of incident atoms due to various demands of the tape will only shift this point either forward or to the rear without affecting anything else except the final optical density of the images, Curves 90 show the background at the several flux rates, while the upper curves show the image deposition at the several flux rates. If unexposed tapes are fed into a development chamber while maintaining a steady efflux from the developer source, the number of available zinc atoms must increase within the volume of the chamber resulting in an excessive incident rate. With the rare exception of the rotating chamber configuration, autonucleation proceeds indiscriminately in the system and suddenly zinc atoms will condense everywhere. At excessive incident rates, the rotating chamber seldom becomes coated and the tape will always pick up the zinc, even though it has not been exposed to electrons. This is made possible by the most favorable arrangement whereby the tape circles the developer source.

FIGS. 5 and 6 show two extremes, in each case utilizing a filament type zinc source. The FIG. 6 is typical for prior art arrangements and large incident rates are required to produce visible images in the shortest possible time. About percent of the atoms may be lost at TV-recording rates, whereas, by using the rotating development chamber, all re-evaporating atoms are collected eventually by other portions of the tape. Of course, a modified development system may be constructed whereby a uniform zinc flux is established over a length of tape. However, this is not a simple approach and requires not only a large area source, as is shown in FIG. 9, but also a sizeable backup surface. Since this zinc reflector is not renewed, it may become coated in time and adsorbs all the zinc available. In comparison, the dead area in the rotating chamber of this invention is quite small, and the developer flux incident upon it is far below critical. Furthermore, the two rotating glass discs, as well as the hub, may be fitted with a stationary wiper or protection means, as shown in FIGS. 7 and 8. This felt-type rectangular wiper block 98 may be soaked in a suitable organic liquid of low free surface energy, thus providing continuous protection for the wiped surface from zinc deposition.

In order to minimize the chance of permanent zinc deposition on the interior surfaces of the discs defining the chamber, and to prevent permanent deposition where the critical conditions have been just reached, protection means can protect a small area of the interior surfaces of the discs. This protection means provides an area in which a vapor flux is not directed at the discs and permits a zone of evaporation without corresponding impingement. The wiper 98 provides such a protected area and would be helpful in preventing zinc buildup, even if it did not contact the discs. Instead of the wiper 98, or additionally to the wiper 98, a disc protection means comprising a stationary thin plate located adjacent to the interior surface of each disc and adjacent to the position of the wiper can be employed. Such a plate might be a truncated circular segment, or pie-shaped piece to provide .protection means for the discs, as discussed above.

The kind of recording medium is not critical. As a matter of fact, anything that has a controlled variation of the surface-free energy upon it may be developed in this manner. The preferred media for electron beam recording/readout in near real time is comprised mainly of photoconduetive and photoemissive pigments combined with a nucleation-inducing compound in a suitable binder. Decomposable compounds yielding nucleation centers of desired configurations upon electron, photon, or ion bombardment may also be utilized.

This invention having been described in its preferred embodiment, and an alternative embodiment also described, it is clear that it is susceptible to numerous modifications and embodiments within the ability of those skilled in the art and without the exercise of the inventive faculty. Accordingly, the scope of this invention is defined by the scope of the following claims.

What is claimed is: V

l. The method of exposing and developing a sensitive material on an indefinite length of moving web to form a latent image on the web and subsequently develop the latent image to a visible image comprising the steps of:

continuously feeding a sensitive medium on a web past an exposure station;

directing exposure energy selectively at the medium as it passes the exposure station to form a latent image on the sensitive medium so that the exposed area of the sensitive medium has a greater heat of adsorption than the unexposed area;

continuously feeding the web to and engaging the web around a pair of axially-aligned rotatable discs so that the latent image faces inward between the discs, and the continuously feeding web rotates the discs and forms the unobstructed circumference of the development chamber;

producing a flux of vaporized developer material between the discs to deposit on the web to develop the latent image and thereby form a visible image.

2. The method of exposing and developing a sensitive material of claim 1 further including the step of protecting a zone between the discs from the flux of vaporized developer material so that the inward surfaces of the discs are protected from the flux as the discs pass the zone.

3. The method of exposing and developing a sensitive material of claim 1 further including the step of con trolling the surface conditions of the inwardly-directed faces of the discs so that the surface concentration of the developer material on those faces of the discs is below 10 atoms/cm*.

4. The method of exposing and developing a sensitive material in accordance with claim 3 wherein the exposure step of the medium is controlled to cause a sufficient increase in the heat of adsorption of the developer material to cause deposition of developer material on the latent image area in excess of about 1O atoms/cm? 5. The method of exposing and developing a sensitive material of claim 4 further including the step of protecting a zone between the discs from the flux of vaporized developer material so that the inward surfaces of the discs are protected from the flux as the discs pass the zone.

6. The method of exposing and developing a sensitive material in accordance with claim 5 further including the step of removing deposited developer material from the inwardly-facing faces of the discs at said zone, 

1. The method of exposing and developing a sensitive material on an indefinite length of moving web to form a latent image on the web and subsequently develop the latent image to a visible image comprising the steps of: continuously feeding a sensitive medium on a web past an exposure station; directing exposure energy selectively at the medium as it passes the exposure station to form a latent image on the sensitive medium so that the exposed area of the sensitive medium has a greater heat of adsorption than the unexposed area; continuously feeding the web to and engaging the web around a pair of axially-aligned rotatable discs so that the latent image faces inward between the discs, and the continuously feeding web rotates the discs and forms the unobstructed circumference of the development chamber; producing a flux of vaporized developer material between the discs to deposit on the web to develop the latent image and thereby form a visible image.
 2. The method of exposing and developing a sensitive material of claim 1 further including the step of protecting a zone between the discs from the flux of vaporized developer material so that the inward surfaces of the discs Are protected from the flux as the discs pass the zone.
 3. The method of exposing and developing a sensitive material of claim 1 further including the step of controlling the surface conditions of the inwardly-directed faces of the discs so that the surface concentration of the developer material on those faces of the discs is below 1014 atoms/cm2.
 4. The method of exposing and developing a sensitive material in accordance with claim 3 wherein the exposure step of the medium is controlled to cause a sufficient increase in the heat of adsorption of the developer material to cause deposition of developer material on the latent image area in excess of about 1014 atoms/cm2.
 5. The method of exposing and developing a sensitive material of claim 4 further including the step of protecting a zone between the discs from the flux of vaporized developer material so that the inward surfaces of the discs are protected from the flux as the discs pass the zone.
 6. The method of exposing and developing a sensitive material in accordance with claim 5 further including the step of removing deposited developer material from the inwardly-facing faces of the discs at said zone. 